Means for observing electron beams



wnvn a no man g- 6, 1963 HIDEO KURODA 3,396,262

MEANS FOR OBSERVING ELECTRON BEAMS Filed Nov. 23, 1964 INVENTOR. 19/0/50 AUAODA BY ds'reazz/w, F4555 Quasi-fin? United States Patent Office 3,396,262 Patented Aug. 6, 1968 3,396,262 MEANS FOR OBSERVING ELECTRON BEAMS l-lideo Kuroda, Tokyo, Japan, assignor to Nippon Electric Company Limited, Tokyo, Japan Filed Nov. 23, 1964, Ser. No. 413,257 Claims priority, application Japan, Nov. 28, 1963, 38/ 89,268 5 Claims. (Cl. 219-121) ABSTRACT OF THE DISCLOSURE Apparatus for permitting the observation of the bombardment of a work piece by an electron beam. The work piece is positioned within a work chamber containing an opening having a transparent window for permitting said observation. The work chamber is formed of a metallic material. A portion of the transparent window is coated on its interior surface with a transparent conductive material which is electrically isolated from the work chamber. A shield is positioned within the interior of the work chamber and surrounds the uncoated portion of the transparent window to prevent collection of charged particles thereon. Bias means are provided for establishinng a slightly positive voltage relative to the potential level of the work chamber to repel positively charged particles. A second transparent conductive coating may be provided on the exterior surface of the transparent window. This coating makes electrical contact with the work chamber to eliminate the presence of an electrical field exterior to the work chamber.

The instant invention relates to electron beam observation means and more particularly to a novel observation window construction for use in devices in which it is most desirable to observe an electron beam bombardment of a work piece which window assembly is so constructed as to prevent its being contaminated during the observation period so as to provide complete and unfettered view of the work piece being bombarded.

In devices which generate electron beams for the purpose of bombarding a work piece it is typical to provide a window or observation means normally having a microscope viewing means in order to observe the surface of the work piece. Heretofore, however, the electron beam machine of the type described generally above had the basic defect of the electron beam undergoing a deflection or bending effect due to the presence of an irregular electric field in the immediate vicinity of the observation window assembly, which is caused by the accumulation of the electric charge formed through evaporation occurring during the bombardment procedure. As a further effect the transparency of the window assembly also undergoes significant deterioration due to the adhesion of metallic evaporation on the surface of the window glass, said evaporation having been caused by the electron beam during the bombardment process thereby making the obscrvation of the work piece ditficult, if not impossible.

In the past a typical remedy applied to overcome such defect has been the use of a shielding shutter or glass filter, or the like. Such contrivances have added additional defects, one of which being that nothing can be seen when such a shutter means is used during the bombarment operation, or it has been impossible to observe the interior of the bombardment chamber due to the gradual straining and loss of transparency of the filter.

The instant invention has as a primary objective that of providing a work chamber having a window assembly which eliminates all of the above defects while providing a window assembly which permits observation of the work piece with the requisite clarity.

The instant invention is comprised of a work chamber having at least one surface provided with an opening therethrough for receiving a Window assembly. The work chamber is preferably formed of a conductive material so as to have the entire surface of the work chamber at one potential. The window assembly is comprised of a transparent window member sealed within the apert-ure provided therefor and having opposing surfaces thereof being at least partially coated with a conductive film which nevertheless has excellent transparency characteristics. The conducting film of the outer surface is electrically connected to the work chamber while the conductive film of the window assembly inner surface is coupled to a potential source placing the inner conductive film at a potential which is just slightly positive relative to the work chamber potential. The window assembly is further provided with means for isolating or shielding the region of the window assembly inner surface which is at a slightly positive potential, from the remainder of the work chamber so as to prevent any film or conductive material which may impinge upon the surface, from establishing an electrical path between the work chamber and the electrical surface so as to destroy or diminish the slight electrical potential provided therein.

The above arrangement thereby provides an apparatus through which the electron bombardment of a work piece may be viewed without any danger of contamination of the window assembly so as to destroy or diminish the visibility of the work piece.

It is therefore one object of the instant invention to provide a novel window assembly for work chambers wherein work pieces are bombarded by electrons.

Still another object of the instant invention is to provide a novel window assembly for chamber means in which work pieces are bombarded with electron rays such that the window assembly provides a continuous clear view of the work piece unaffected by the electron bombardment or the secondary emission caused by the electron bombardment.

Still another object of the instant invention is to provide a novel window assembly for use in work chambers and the like in which work pieces are bombarded with electron beams wherein said window assembly is provided wtih means for preventing the contamination of the window assembly due to bombardment of the work piece by electron beams.

Still another object of the instant invention is to provide a novel window assembly for use in work chambers and the like in which work pieces are bombarded with electron beams wherein said window assembly is provided with means for preventing the contamination of the window assembly due to bombardment of the work piece by electron beams and further providing means for preventing any effect or deflection of the electron beam employed for bombardment due to possible charge collection upon the window assembly.

These and other objects of the instant invention will become apparent when reading the accompanying description and drawings in which:

FIGURE 1 is a vertical section showing one embodiment of the instant invention.

FIGURE 2 shows the window assembly of FIGURE 1 in greater detail.

Referring now to the drawings, FIGURES 1 and 2 show an electron beam apparatus 10 comprised of a source of an electron beam 11 generating the electron beam 13. The electron beam 13 is guided through a tube or passageway 14 which is provided with an electron focusing lens which is also commonly referred to as a focusing coil employed for the purpose of providing a pencil beam (i.e., a beam of relatively narrow diameter or cross-section). The electron beam moves in a downward vertical direction as shown by arrow 16 so as to impinge upon the work piece 17 which is placed upon the base 18a of a work chamber generally designated as 18. The electron beam source 11 communicates with the work chamber 18 through an opening 18b provided within the work chamher.

The work chamber 18 is further provided with a surface 180 which is angularly disposed to the vertical direction. This surface 180 is provided with an opening 18d which in turn, is provided with a window assembly 20 through which the bombardment of the work piece 17 by the electron beam 13 may be observed.

During the bombardment operation the impinging of high velocity electrons from beam 13 upon work piece 17 causes a secondary emission effect such that evaporation (i.e., positively and negatively charged particles represented generally by the numeral 21) are caused to be emitted from the surface of the work piece 17 undergoing electron bombardment. A large number of these particles, mostly those which are positively charged, reach the inner surface of the window assembly 20 and have a tendency to cause an electrical charge to be collected upon the inner surface of the window assembly 20, which electrical charge sets up a field having an unfavorable effect upon electron beam 13 and thereby causing the electron beam to deflect from its normal path contrary to the desire of the operator. In addition thereto, the metallic evaporation which adheres to the inner surface of the window assembly will deteriorate the transparency qualities of the window glass so as to greatly impair the ability of an operator to observe the work piece under electron bombardment.

The instant invention provides a novel window assembly 20 which very favorably acts to overcome these disadvantages.

The window assembly 20 is comprised of a transparent window member 22 which is set in the opening 18d in work chamber 18. The outer surface of window 22 (i.e., that surface which is subjected to normal atmospheric pressure) is coated with a conductive coating or film 30 such as tin dioxide (usually called Nesa) which has excellent conductive characteristics and concurrently therewith excellent transparency characteristics. The window member 22 may preferably be lead glass. It should be understood that these materials are merely preferred choices and any other suitable materials may be substituted therewith. The conductive coating 30 covers the entire surface of the transparent member 21 and makes electrical engagement with the work chamber 18 so as to be at the same potential as the chamber. The chamber 18 is formed of a suitable conductive material so as to have substantially the same potential at any point around the work chamber. Thus, regardless of the voltage level within the work chamber itself, no electric field is set up exterior to the work chamber. As one form of viewing means a microscope means 23 is shown in schematic form in FIGURE 1 which may, for example, be employed to observe the work piece 17 as it undergoes electron bombardment.

Referring again to the window assembly 20 and more particularly to the detailed structure of FIGURE 2, the window assembly 20 is further provided with a conductive coating 24 along the interior surface thereof which may be a layer of tin dioxide, as mentioned previously. It should be understood that any other suitable material having good conductivity and transparency characteristics may be substituted therefor.

It should be noted that the conductive layer 24 is applied to the inner surface of the transparent member 22 so as to be physically and therefore electrically spaced from the work chamber 18. This leaves the conductive coating 24 free to achieve any voltage level.

Due to the fact that the particles forming the evaporation or secondary emission 21 shown in FIGURE 1 are predominately positively charged bodies, this leaves the conductive coating 24free to be impinged upon by such charged bodies and thereby collect and develop a charge along the surface thereof. Such positive charge, given an opportunity to develop, will set up an electric field which can react with the electron beam 13 to deflect the beam, against the actual wishes of the operator, thereby affecting the bombardment operation.

In order to avoid this disadvantage a voltage source 25 is provided within the work chamber 18 and has its negative terminal electrically connected to the work chamber 18 at 25a and has its positive terminal electrically connected to the interior conductive coating 24 at 25b. The magnitude of the voltage source is selected to be relatively small so that just a slight positive voltage exists at the conductive surface 24 relative to the work chamber 18. The slight positive voltage, however, is sufficient to repel positive charged bodies thereby preventing such bodies from collecting along the surface of conductive coating 24. The value of electrically isolating the conductive coating 24 from work chamber 18 can now be seen since to do so would destroy the effectiveness of the voltage source 25 in aiding the window assembly to repel positive charged bodies.

In the region of the transparent member 22 which is not covered by conductive coating 24, there is still a possibility that positive charged particles can adhere to this region and hence bridge an electrical path between conductive coating 24 and work chamber 18. This phenomenon is prevented from occurring by means of the provision of shields 26 and 27, respectively. The upper shield 26 is physically secured to the work chamber 18 above the upper end of window assembly 20 and has an extending flange 26a which shields the uncoated upper region of transparent member 22 from charge particles which may be moving in that general direction. Likewise, the lower shield 27 (omitted from FIGURE 1 only for purposes of simplifying the figure) is physically connected to the work chamber 18 in the region beneath the lower end of transparent member 22 and is further provided with an extending flange 27a which shields the lower marginal region of transparent member 22 which is not provided with the conductive coating 24. It should be understood that (if the window is rectangular in configuration) the entire marginal region of the transparent member 22 would be free of any conductive coating and further that the shields 26 and 27 completely surround the window at its periphery so as to prevent the adherence to and collection of charge particles which may set up an electrical path between the conductive coating 24 and the work chamber 18. The transparent member 22 is securely held within the opening 18d in work chamber 18 and hence is sealed from exterior atmospheric conditions by a suitable O-ring 28 which is provided within a groove 29 which is formed between the work chamber opening 18d and the transparent member 22.

The slightly positive voltage source 25 very effectively acts to repel positively charged bodies against collecting upon the surface of the window member 22 and the shields 26 and 27 further act to prevent charged particles from collecting .on the surface region of the window member 22 which is not provided with a conductive coating. This shielding function, in addition to preventing the window from becoming contaminated and hence keeping the transparency characteristics of the window assembly 20 at a high level, further prevents the collection of charge .on the inner surface of the transparent member 22 which may act to deflect the electron beam 13.

While the slight positive voltage level applied to the conductive surface 24 by means of voltage source 25 may have a slight influence upon the electric field, it should further be understood that this voltage level will be substantial uniform across the conductive coating and hence very easily be compensated for if any compensation is required at all, whereas in the case of charge particles collecting upon the surface of the transparent member 22 may occur in a very irregular or non-uniform fashion so as to be very difficult to be compensated for.

It can therefore be seen that the instant invention provides a novel window assembly for use in electron bombardment devices which has extremely good transparency characteristics and which is prevented from collecting a charge due to the impingement of charge particles which may act to deflect the electron beam in an undesired manner.

In cases where the rate of evaporation is small, it is possible to eliminate the need for a voltage source and simply place the interior conductive coating 24 in electrical contact with the work chamber 18 so as to be at the same electrical potential. When the potential of the transparent conductor film 24 and that of the wall of the work chamber 18 is made equal no distortion phenomenon of the electron beam will occur. Thus, in the case where evaporation rates are low, the voltage source 25 may be eliminated and in the case of high evaporation rates the voltage source 25 is selected so as to make the conductive coating 24 slightly more positive than the interior wall of work chamber 18. It should be understood that in all cases, i.e., in cases of either high or low evaporation rates, the work piece 17 is preferably maintained at the same electrical potential as the wall of the work chamber 13.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. Means for use in bombarding a work piece with an electron beam comprising an evacuated work chamber formed of a conductive material for receiving a work piece; said work chamber having at least first and second openings; said first opening positioned in a first surface of said chamber for passage of an electron beam to bombard the work piece supported upon a second opposing surface of said chamber; said second opening being provided in a third surface of said work chamber positioned between said first and second surfaces to facilitate observation of the bombardment operation; transparent window means positioned within said second opening; means for sealing said window to said chamber; a transparent conductive coating covering a portion of the window means on the interior side of said work chamber to prevent deterioration of the window means transparency; said coating being electrically isolated from said work chamber; shielding means surrounding said second opening and being secured to the interior of said work chamber; said shielding means including a flange lying a spaced distance away from said window for shielding the uncoated surface portion of said window from deposition of charged particles; first means coupled between said work chamber and said conductive coating for repelling charged particles from being deposited upon said conductive coating.

2. The device of claim 1 wherein said first means comprises adjustable voltage means connected between said conductive coating and said work chamber for placing said coating at a slightly positive voltage relative to said work chamber.

3. The device of claim 1 further comprising second transparent conductive coating means on the exterior surface of said window means and being electrically connected to said work chamber to create a zero electric field outside of said work chamber.

4. The device of claim 3 wherein said transparent window means is comprised of lead oxide.

5. The device of claim 3 further comprising an electron beam source; second chamber means connected between said first opening and said electron beam source for guiding the electron beam toward the work piece; focusing means surrounding said second chamber for focusing the electron beam as it moves toward the work piece.

References Cited UNITED STATES PATENTS 2,944,172 7/1960 Opitz et al 219121 3,092,727 6/1963 Leinhos et al. 2l9-121 3,134,013 5/1964 Opitz et al 219-121 3,156,810 11/1964 Samuelson 219--121 3,169,183 2/1965 Radtke et al. 219121 3,322,930 5/1967 Sciaky 219-121 RICHARD M. WOOD, Primary Examiner.

W. D. BROOKS, Assistant Examiner. 

